In instrumentation displays, devices such as air core gauges are used to indicate measures of parameters through varied rotation of pointers, which are viewed against graphic displays. In the manufacture of these instrumentation devices, the pointer is attached to a spindle of the gauge in a process called staking. Fundamentally, staking involves simply pressing the pointer onto the spindle in a desired manner. During the staking process, it is desired to limit the amount of force necessary to press the pointer onto the spindle. If excess force is required to stake the pointer to the spindle, damage to the pointer or the rest of the instrumentation device may result.
FIG. 1 is an illustration of a prior art spindle 16 and pointer shaft 10. The circular cylinder-shaped spindle 16 fits into the circular cylinder-shaped opening 14 of the pointer shaft 10 to provide a friction or press fit. The outer surface 15 of the spindle 16 contacts the inner surface 12 of the pointer shaft 10. The amount of force required to press the pointer shaft 10 onto spindle 16 is proportional to the amount of surface area contact between surface 15 and surface 12. The amount of force required to press pointer shaft 10 onto spindle 16 is also related to the interference of the pointer and spindle diameters, surface finish quality, coefficients of friction, etc.
FIG. 2 illustrates a force/engagement distance diagram for the staking of the prior art pointer and spindle shown in FIG. 1. The trace 17 shows that, as the the pointer shaft 10 is pressed further onto spindle 16, the force required to continue pressing the pointer shaft 10 on the spindle 16 increases.
FIG. 3 shows a prior art pointer shaft 18 that limits the force necessary for staking between the pointer shaft 18 to the spindle 16. During the staking process, the opening 19 is placed over spindle 16. The outer surface 19 of the spindle engages with the surface 20, the pointer shaft 18 The area of engagement is limited, however, as surface 22 of the pointer shaft is recessed from the surface 20 and does not engage the spindle 16.
Construction of the prior art pointer is shown in FIG. 3 can be fairly complex. The pointer shaft 18 must be molded with an extra mold pin or machined from opening 24 in order to provide the recessed surface 22. A cap (not shown) must then be placed on the pointer to hide the hole at opening 24 from a person viewing the instrumentation device.